1. Field of the Invention
The present invention relates to a backlight unit and a method of manufacturing a diffuser used in the backlight unit. More particularly, the present invention relates to a backlight unit for enhancing the diffusion characteristics of a diffuser included in the backlight unit and a method of manufacturing the diffuser.
2. Description of the Related Art
An organic electroluminescent device is self light emitting device that emits light having a certain wavelength. Further, a liquid crystal display (LCD) displays an image using a change in a transmissivity of liquid crystals included in the LCD. Also, because the LCD is not a self light-emitting device, the LCD includes a backlight unit (BLU).
In more detail, FIG. 1 is a sectional view illustrating a BLU 100 included in the LCD, and FIG. 2 is a sectional view illustrating a diffuser used in the BLU 100 in FIG. 1. As shown in FIG. 1, the BLU 100 is driven by a direct-lighting method and includes a light source unit 110, a transparent plate 120 and an optical film 140. Further, the light source unit 110 includes a plurality of light sources 112 for emitting light having a certain wavelength and a light source reflector 114 in which the light sources 112 are located.
In addition, the transparent plate 120 has a predetermined pattern, and is generally made of poly methyl meta acrylate (PMMA). The function of the transparent plate 120 is as follows. When the direct-lighting type BLU 100 does not include the transparent plate 120, a viewing user may actually see white lines in the display caused by the shape of the light sources 112 (hereinafter, referred to as disposition shape of the light sources). Accordingly, the BLU 100 uses the transparent plate 120 so the user does not see the disposition shape of the light sources 112.
In addition, as shown in FIG. 1, the optical film 140 includes a diffuser 142, a prism sheet 144, a protection sheet 146 and a reflective polarization film 148. Further, light transmitted from the transparent plate 120 is incident on the diffuser 142. The diffuser 142 diffuses or condenses the light transmitted from the transparent plate 120 so as to maintain a constant brightness of the BLU 100 and increase the viewing angle of the LCD.
Also, as shown in FIG. 2, the diffuser 142 includes a base film 150, a first diffusion layer 160 and a second diffusion layer 170. The first diffusion layer 160 is formed by coating a first resin 164 having first beads 162 on the upper surface of the base film 150. In addition, the second diffusion layer 170 is formed by coating a second resin 174 having second beads 172 on the lower surface of the base film 150. As shown in FIG. 2, a portion of each of the first and second beads 162 and 172 projects outside of the first and second resins 164 and 174. Thus, the light incident to the diffuser 142 is refracted by the beads 162 and 172, and then is transmitted in a direction of the prism sheet 144.
Referring back to FIG. 1, the prism sheet 144 condenses a light diffused or condensed by the diffuser 142 in a direction of the protection sheet 146, thereby enhancing the brightness of the BLU 100. Further, the protection sheet 146 is located over the prism sheet 144 to protect the prism sheet 144 from dust, etc., and to increase the viewing angle of the LCD narrowed by the prism sheet 144.
Also, only some light provided from the BLU 100 is transmitted through the panel (not shown). For example, a specific polarized light, e.g., aP wave of the light provided from the BLU 100 is transmitted through the panel, and the other polarized light, e.g., an S wave of the light is absorbed by the panel. Accordingly, the reflective polarization film 148 is employed in the BLU 100 so as to use the other polarized light absorbed by the panel.
In addition, the reflective polarization film 148 reflects the other polarized light diffused by the protection sheet 146 in the direction of the light source unit 110, and provides the specific polarized light to the panel. Further, the other polarized light reflected by the reflective polarization film 148 is again reflected by the light source reflector 114. As a result, the reflected other polarized light is changed into light including a specific polarized light and the other polarized light. The changed light is again incident to the reflective polarization film 148 through the diffuser 142, the prism sheet 144 and the protection sheet 146.
Thus, the BLU 100 enhances the efficiency of the light using the above described method. That is, the BLU 100 diffuses the light emitted from the light sources 112 using the transparent plate 120 and the diffuser 142 so that the user does not see the disposition shape of the light sources 112. However, the diffuser 142 does not sufficiently or uniformly diffuse the light emitted from the light sources 112. Accordingly, the user may still see the white lines in the display cause by the disposition shape of the light sources 112. In addition, the manufacture cost of the transparent plate is increased because the BLU 100 uses the transparent plate 120 having a predetermined pattern.